Quercus opaca Trel.

Mexico (Hidalgo, Nuevo Leon, San Luis Potosi, Tamaulipas); 1200-2000 m;

not exceeding 2 m tall, usually 0.6 m;

2.5-4.5 cm long, 1-1.5 cm wide; evergreen; subleathery; oblong, lanceolate to elliptic; apex acute, obtuse or rounded, mucronate; base obtuse to cordate, sometimes rounded; margin thickened, flat or remotely revolute, most often entire, or with 1-3 pairs of sharp mucronate teeth near apex; glaucous adaxially, dull, glabrescent (scarce stellate trichomes at base of the midvein); beneath not lustrous, glaucous, almost glabrous except some sessile stellate trichomes and white glandular hairs mainly on midvein; epidermis markedly whitish papillose; 6-10 vein pairs flat above, slightly raised beneath; petiole 3-7 mm long, pubescent, reddish brown;

male catkins 3-4 cm long, with many flowers;

acorn ovoid, glabrous, ca. 9 mm long, included 1/3 in the cup; solitary or paired on a glabrescent peduncle 0,5 cm long; cupule halfround slightly tomentose; maturing first year, in September;

Mexican Plateau, in arid tropical scrub.

– A.Camus : 177; – Sub-genus Quercus, Section Quercus, Series Leucomexicanae, Group Opacae; – Closely related to Q.pringlei . – Q. opaca can be confused with Q. sebifera and Q. pringlei. It can be deistinguished from Q. sebifera by its oblong, elliptic or lanceolate leaves and the abaxial blade surface is not waxy; Q. sebifera has obovate leaves and the abaxial blade surface is waxy. Q. pringlei differs from Q. opaca in having narrower, oblong or narrowly-elliptic and bicolored leaves, the adaxial surface is olive green and shiny, while the abaxial surface is pale and dull.